Ah - can handle a camera with focus then
(I know my son at 5 works best with a fixed focus camera, so did want to check )
If he's used to disposable cameras and is likely to take it places it might get damaged or broken, I'd recommend having a look in places like Tesco or bargain bins in various discount outlets. You can get some great (fairly basic though) cameras with brand names I've never heard of around the £30-40 mark that are great value, and the best thing is that if it gets lost or broken it doesn't really matter.
If he really wants a better make or model, I can really recommend the Canon Powershot series as great cameras, packed with features and good quality lenses and build.
Pixmania do the Canon Powershot A530 for £116 which is a fab price for a great little 5 Megapixel camera. If he didn't want to buy it online, chances are if he printed off the offer and walked into Jessops they'd pricematch for him.
Or if you wanted under £100, then Pixmania also stock the A430 in various different colours at £99 - 4 Megapixels but still a fairly nice spec for the money.
In all cases he will almost certainly need to buy a larger memory card, so do factor that into the budget - cameras are sold with terribly piddly sized cards that are no good for man nor beast.
Hope that's helped